A flow control valve, for example, effects a control of a control fluid operating inside a displacement-type compressor and a discharge fluid discharged therefrom by means of valve opening/closing actions. The discharge fluid contains ferrous particles or aluminum particles caused by abrasion during the operation within the displacement-type compressor. Silicon particles contained in liquid glass which is used for a displacement-type compressor are also mixed into the discharge fluid during the operation. Diameter of these particles is approximately 10 micrometer so that they are apt to get stuck between the slide surfaces. Since the particles stuck between the slide surfaces of the valve rod in the flow control valve are likely to cause a trouble in operation, how to solve it has been an immediate concern. There is a solution to the problem in which a filter is disposed before the fluid is introduced into the flow control valve in order to collect the particles. Disposing the filter, however, causes a rapid loading of the filter, thereby deteriorating the performance of the flow control valve. Also as the loading of the filter increases the pressure of the control fluid inside the piping, the control of the flow control valve is made difficult. At any rate, the fine particles contained in the operating fluid of the flow control valve deteriorate the operation of the valve rod. Therefore resolving this problem is of vital importance.
Further details will be described below. There is a flow control valve for a variable displacement compressor as prior art of the present invention. For example, there are a patent reference 1 and patent reference 2 given below. A valve body is disposed in the operating valve rod of the flow control valve. This valve rod executes valve opening/closing actions by means of operating with the solenoid rod of a solenoid portion which is connected with the valve rod. And the valve rod is guided under operation by a fit engagement surface which is disposed in the valve housing.
The above prior art is explained-further below. A flow control valve 100 in FIG. 5 is similar to the flow control valve disclosed in FIG. 1 of the patent reference 1 or FIG. 1 of patent reference 2 given below. This flow control valve 10 is comprised of a valve main body 110, a pressure-sensing device 120 and a solenoid portion 130. A valve housing 111 which defines the outer profile of the valve main body 110 disposes a through bore which extends therethrough in axial direction thereof. This through bore disposes a guide bore surface 111A and a valve chamber 115 therein. The valve chamber 115 receives a discharge port 103 which extends through side wall thereof. The guide bore surface 111A also receives a control port 104 for a control fluid which extends through side wall thereof. There is also disposed a pressure-sensing chamber 122 to the lower portion of the guide bore surface 111A as shown in the figure which communicates with the through bore. There is also disposed a suction port 105 in the valve housing 111 which communicates with the pressure-sensing chamber 122.
A pressure-sensing device 120 is disposed in the pressure-sensing, chamber 122. This pressure-sensing device 120 contracts or stretches according to the suction pressure Ps of the fluid introduced from the suction port 105 into the pressure-sensing chamber 122. This pressure-sensing device 120 is connected with the valve rod 108.
There is disposed a solenoid portion 130 in the upper portion of the valve main body 110 in the figure. The solenoid portion 130 then disposes a fixed iron core (also referred to as fixed core) 131 and moveable iron core (also referred to as moveable core) 133 therein. There is a solenoid coil surrounding the fixed iron core 131 and the moveable iron core 133. A magnetic field generated in accordance with the current supplied to the solenoid coil creates a mutual attraction force. A solenoid rod 133A connected with the moveable iron core 133 is connected with a valve rod 108. A rod guide bore 131A which fittingly mates a first slide rod 106 of the valve rod 108 in freely moveable manner is disposed in the fixed iron core 131.
This valve rod 108 disposes a valve portion 102 to a first slide rod 106. There is also disposed a connection rod which is a lower part in the figure of the valve portion 102 of the valve rod 108 and smaller in diameter than the first slide rod 106. A passageway 116 is defined between the connection rod and the guide bore surface 111A. The discharge port 103 and the control port 104 come to a direct communication via passageway 116 when the valve portion 102 opens. The communication between the discharge port 103 and, the control port 104 is shut off when the valve portion 102 is in a closing position. A portion of the valve rod 108 further closer to the pressure-sensing device 120 forms a second slide rod 107. Outer circumferential surface 107A of the second slide rod 107 forms a freely moveable fit engagement with the guide bore surface 111A. The fit engagement of the second slide rod 107 relative to the guide bore surface 111A shuts out a communication between the suction port 105 and the control port 104. Guide provided for the first slide rod 106 and the second slide rod 107 by means of small clearance gap formed relative to the rod guiding bore 131A and the guide bore surface 111A makes it possible for the valve portion 102 to rest on a valve seat in a seal-tight manner.
In the flow control valve 100 thus configured, FIG. 4 is an enlarged view for explaining the problem encountered in FIG. 5. The discharge fluid F introduced or discharged from the discharge port 103 contains ferrous particles, aluminum particles or silicon particles. These particles are fine particles whose diameter ranges from 10 micrometers to 20 micrometers. A fine particle P, as shown in FIG. 4, gets caught between the fit engagement surface of the first slide rod 106 and rod guiding bore 131A. Then when the first slide rod 106 and the second slide rod 107 are tilted away from the axis line, a portion of the fit clearance above the fine particle P in the figure becomes narrower. This leads to that the fine particle P will be accumulated in the fit clearance gap between the first slide rod 106 and the rod guiding bore 131A even when the discharge fluid F under discharge pressure Pd forms an upstream flow. When the valve rod 108 tries to operate, the fine particle P squeezed in the fit clearance gap between the first slide rod 106 and the rod guiding bore 131A hampers the prescribed operation of the valve rod 108. Therefore it becomes difficult to control the control fluid as desired in the flow control valve 100.
Patent reference 1: Japanese Patent Laid-Open Publication No. 2001-248761 (FIG. 1)
Patent reference 2: Japanese Patent Laid-Open Publication No. 2002-31052 (FIG. 1)